Granular (FePt)(1 -) (y)(SiNx)(y) (y = 0-63 vol.%) nanocomposite thin films are fabricated by dc and rf magnetron co-sputtering of Fe, Pt and SiNx targets, then annealed at different temperatures and times. As the SiNx contents raise to 39 vol.%, the (FePt)(1) (-) (y)(SiNx)(y) film has maximum out-of-plane squareness (S) and the largest out-of-plane coercivity (Hc), they are 0.99 and 21.2 kOe respectively. Saturation magnetization of the (FePt)(1) - (y)(SiNx)(y) film is inversely proportional to the SiNx content. From the field emission gun high resolution transmission electron microscope analysis, it is shown that the grain size of (FePt)(37)(SiNx)(63) film is about 4 nm. And the Hc, S, and the in-plane squareness (S-11) values of the (FePt)(37)(SiNx)(63) film are 6.5 kOe, 0.75, and 0.45, respectively. (C) 2009 Elsevier B.V. All rights reserved.